Seeders suitable for direct drilling, which are designed for sowing on fields that have not first been prepared by cultivating implements, and on which plant stubble remaining from previous harvesting process and other impurities are present, require sufficient pressing forces for their furrow openers. These pressing forces are necessary in order to produce a sufficiently deep seed furrow and possibly a fertilizer furrow and to push aside or cut through the plant parts and other materials still present on the field.
In the prior art (cf. EP 2 517 545 A1, for example), such seeders suitable for direct drilling are generally equipped with a frame of their own, which is supported on wheels and pulled across the field by a towing vehicle (generally a tractor). A seed container, which supplies the individual sowing units supported on the frame, is mounted on the frame. The seed is transported pneumatically from the seed container to the sowing units. The seeder itself has a sufficiently high weight that it causes no problems to provide the forces necessary for introducing the furrow into the ground by means of springs and/or hydraulic or pneumatic actuators, which are arranged between the furrow opener (or a sowing unit, on which the furrow opener is mounted), and the frame. The force necessary for opening the furrow is transmitted by the spring or the actuator onto the frame of the seeder.
DD 204 827 A1 describes a seeder with spring-loaded sowing colters mounted on the three-point hitch of the tractor. The weight of the seeder is borne by wheels of the seeder during the sowing process. To increase the load on the front wheels of the tractor during the turning process or to adjust the pressing force of the sowing colter, the seeder can be pivoted forward and upward relative to the three-point hitch by means of a hydraulic cylinder. The pressing force for the sowing colter (not expressly suitable for direct drilling) is likewise provided by the of the seeder's own weight.
It is therefore considered undesirable that a high weight of the seeder itself was required in the prior art in order to provide the pressing force for the furrow opener. It would be desirable, however to provide a lighter-weight seeder, which is nevertheless suitable for direct drilling.